Reversible motor hydraulic control system

ABSTRACT

A hydraulic control system is provided comprising essentially a reversible electric motor-pump which drives a hydraulic actuator. The hydraulic system includes a compensator shuttle valve coupled to a reservoir for compensating for the unequal displacements in the actuator and feeding the pump. A starting switch is provided for operating the motor in one direction, and the hydraulic system functions to store and impart a starting torque of opposite rotational sense each time the motor is brought to a momentary stall condition under load, thereby reversing the motor and the pump driven thereby. In one embodiment, on the return stroke the cylinder is allowed to touch bottom in the actuator, which again provides a torque reversal for reversing the direction of motor rotation. The cycle is repeated as long as power is applied to the motor, with no manual, electrical or hydraulic switching. In another embodiment, a single stroke return-and-stop operation is provided, utilizing a limit switch to remove power on the motor at the termination of the return stroke of the cylinder.

[451 Dec.24, 1974 REVERSIBLE MOTOR HYDRAULIC CONTROL SYSTEM MarioQuinto, 7O Dannell Dr., Stamford, Conn. 06905 Filed: Aug. 24, 1973 Appl.No.: 391,234

Inventor:

7/1960 Ashton 11.. 60/470 9 1935 Ernst 60/380 [57] ABSTRACT A hydrauliccontrol system is provided comprising essentially a reversible electricmotor-pump which drives a hydraulic actuator. The hydraulic systemincludes a compensator shuttle valve coupled to a reservoir forcompensating for the unequal displacements in the actuator and feedingthe pump. A starting switch is provided for operating the motor in onedirection, and the hydraulic system functions to store and impart astarting torque of opposite rotational sense each time the motor isbrought to a momentary stall condition under load, thereby reversing themotor and the pump driven thereby. In one embodiment, on the returnstroke the cylinder is allowed to touch bottom in the actuator, whichagain provides a torque reversal for reversing the direction of motorrotation. The cycle is repeated as long as power is applied to themotor, with no manual, electrical or hydraulic switching. In anotherembodiment, a single stroke return-and-stop operation is provided,utilizing a limit switch to remove power on the motor at the terminationof the return stroke of the cylinder.

7 Claims, 3 Drawing Figures PATENTED UEB24I974 sum 1 OF 2PATENTEBUEBZMQH 855 9 sum 2 0f 2 FIG.

REVERSIBLE MOTOR HYDRAULIC CONTROL SYSTEM BACKGROUND OF THE INVENTIONThis invention relates to a hydraulic control system, and moreparticularly to a reversible motor hydraulic control system forautomatically and rapidly reversing the flow of hydraulic fluid andcylinder action in such a system.

Many hydraulic systems have been provided for controlling the operationof a cylinder in a hydraulic actuator by means of a reversible pumpwhich provides a reversible fluid supply acting through some form ofcontrol valve. The usual method of reversing flow in such a system is touse a pump and motor and to divert the fluid flow from one side of anactuator to another by means of a four-way valve which is actuatedeither electrically or mechanically. Such systems are complex andgenerally require a variety of components, e.g. check valves, reliefvalves, pressure switches, etc., which make the systems difficult tooperate and maintain. The reversal operation usually requires a manualoperation of an operator or a switch and four-way directional valve toaccomplish the desired result.

Accordingly, it is an object of the present invention to provide a newand improved hydraulic control system which automatically reverses theflow of fluid in such a system with a minimum of components and operatoreffort.

SUMMARY OF THE INVENTION In carrying out this invention in oneillustrative embodiment thereof, the hydraulic control system isprovided having a reversible motor and an electrical circuit for theoperation of the motor, and a hydraulic system having a reversible pumpfor driving a hydraulic actuator. In the hydraulic system, a compensatorshuttle valve is coupled to a reservoir and to the reversible pump andhydraulic actuator for equalizing forward and return cylinderdisplacements in the actuator. Fluid reversal in the system isaccomplished by reversing the rotation of the motor pump assembly, whichis accomplished by the matched dynamics of the hydraulic load. Thehydraulic system stores enough energy to impart an initial startingtorque of opposite rotational sense each time the motor is brought to astall condition under load, thereby reversing the motor and pump. In oneembodiment, on the return stroke of the cylinder, the cylinder isallowed to touch bottom in the actuator, which again provides a torquereversal for reversing the direction of motor rotation. The cycle isrepeated as long as power is supplied to the motor, with no manualelectrical or hydraulic switching.

In another embodiment, a single stroke return-andstop operation isprovided, utilizing a limit switch to remove power on the motor at thetermination of the return stroke of the cylinder in the hydraulicactuator.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of oneform of electrical control circuit, together with the driven hydraulicsystem shown in one operating position.

FIG. 2 is a schematic of the hydraulic system shown in FIG. 1, operatingin a reverse direction from that shown in FIG. 1.

FIG. 3 is an electrical schematic diagram of another embodiment of anelectrical control circuit.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, ahydraulic system in accordance with this invention is illustrated in oneoperative position on the right side of the figure, while one form ofelectric control circuit is shown on the left side of the figure. Sincethe electrical control circuits may be varied, and two embodimentsthereof are shown in FIGS. 1 and 3, the hydraulic portion of the systemwill be described first, and like elements will be designated with thesame reference numerals throughout the drawings.

The hydraulic control system illustrated on the right side of FIG. 1 iscomprised basically of a reversible pump 10, a compensator shuttle valve12, a reservoir 20 containing a supply of hydraulic fluid 25, ahydraulic actuator 35 for driving a work ram 40, and suitableinterconnecting hydraulic lines. The reversible pump 10 is coupled by aline 28 to the blind end 33 of the hydraulic actuator 35 and by a line30 to the rod end 37 of hydraulic actuator 35. The compensator shuttlevalve 12 is comprised of two opposing poppet valves 14 and 16,mechanically linked together by a rod 18. The compensator shuttle valve12 incorporates three ports, one of which is connected by a line 22 tothe reservoir 20, and the other ports are connected by a line 24 to line28 and by a line 26 to line 30, and are alternately opened, depending onthe direction of fluid flow, and accordingly the direction of therotation of the reversible pump 10. The compensator shuttle valve 12replaces the normal use of four check valves to accomplish the sameresult. The hydraulic actuator 35 has a piston 36 and a rod 38 which isconnected to and used for driving a work ram 40. The system utilizes theinertia of the motor coming to a stall against a load in order to obtainthe desired force to perform the work without requiring a much largerelectric motor. Thus in a typi-- cal example, a A: hp. motor can beemployed where normally a 3 hp. motor would be required for one type ofgarbage compactor. The flexibility and energystoring capacity of thehydraulic system is referred to as an accumulator. Depending on theapplication of the system and the stored energy requirements, additionalaccumulators 32, coupled to line 28, and/or 34 coupled to line 30, maybe provided in the form of a bellows, a spring with piston arrangements,longer or larger diameter hydraulic lines, or any other suitable meansfor applying any additional energy storing ability required.

One form of electric control circuit is shown on the left side of FIG.1, which primarily functions to start and control a reversible electricmotor which drives the reversible pump 10. Any single phase reversiblemotor may be employed utilizing the required voltage for that type ofmotor, for example 110, 220, or 440, and the selection of the motor willdepend upon the application of the hydraulic control system. The type ofmotor illustrated in FIG. I is a capacitor start type, with the motor 70having a rotor 72, a field operating winding 74, and a start orauxiliary winding 76 in series with a capacitor 78. Power for the motor70 is derived from an electrical plug 50 which is connected to asuitable electric outlet with the desired source of power. The powerline is provided with a fuse 52 and a bidirectional semiconductor switch54, called a triac, which is connected to the operating winding 74 ofthe motor 70, and through a resistance 58 to contacts of a start switch60. The start switch 60 is a momentary-on type having contact pairs 65and 67. The closure of the momentary on-switch 60 closes contacts 65which operate a latching relay 64, and closes its contact 66 in latchingengagement until deactivated by a stop-switch 62. A manual reversalswitch 56 having contacts 57, 59, 61 and 63 is connected across thestarting winding 76, capacitor 78, and a bidirectional switch 84. Alsoconnected across the starter winding are a centrifugal switch 80 and aresistor 82. The manual reversal switch 56 functions merely to reversethe starting winding to drive the motor 70 in a reverse direction whenactuated, and will be used when the work ram is stuck or in anysituation when a motor reversal is manually desired.

In the operation of the electric circuit shown in FIG. 1, when the startswitch 60 is depressed, closing the contacts 65 and 67, power is appliedthrough the closed contacts 57 and 61 of the manual reversal switch 56to the starter winding 76. Also, the closing of contacts 65 activatesthe latching relay 64 and closes its contact 66, which switches on thetriac switch 54 to put power on the operating winding 74 of the motor70. The triac 54 carries the motor load current, limiting the amount ofcurrent handled by the remaining circuit switches. Similarly, the triac84 in the motor start circuit carries the motor starting quadraturecurrent, and the centrifugal switch 80 in the motor, which is normallyopen until the motor starts, must make and break only 1/50 of the startwindings current. This feature will normally extend motor life to thelimit resulting from bearing fatigue. To utilize the manual reversalswitch 56, both the start switch 60 and 56 must be actuated together toaccomplish the desired reversal, and then the stop switch 62 isdepressed when it is desired to manually stop the operation.

In the operation of FIG. 1, fluid reversal is accomplished by reversingthe rotation of the motor 70, and accordingly the pump 10. Normalreversal is accomplished by the matched dynamics of the hydraulic loadin which the accumulator action of the system stores enough energy toimpart an initial starting torque of op posite rotational sense eachtime the motor 70 is brought to a stall condition under load. A normalworkproducing stroke of the ram 40 consists of the application of powerto the motor 70 with its starting winding 76 phased to produce highpressure on the blind side 33 of the hydraulic actuator 35, providingstored energy in the accumulator 32. To start the operation, themomentary start switch 60 is depressed, which closes the latching relay64 and associated contacts 66 to actuate the starting winding 76 andswitch on the triac switch 54 to put power on the operating winding 74of the motor 70. This action drives the pump in the direction indicatedby the arrows on FIG. 1. The blind end 33 of the hydraulic actuator 35has a higher volumetric displacement than the rod end 37 because of rodvolume. The difference in flow due to rod volume is not sufficient tomaintain the desired output flow, and accordingly it is necessary forthe pump 10 to draw fluid 25 from the reservoir through the shuttlevalve 12 to make up the difference. The shuttle valve 12 is driven bypressure differential which opens the port associated with the poppet 16to provide fluid in the direction shown from the reservoir, whichcreates an automatic replenishing system. Fluid is also drawn from therod end 37 of the actuator 35. As fluid is supplied by the pump 10 fromthe rod end 37 and the reservoir 20 through the open port of poppetvalve 16 to the blind end 33, the piston 36 and its connected rod 38move downward, driving the work ram 40 downward. This forward stroke isterminated by force, or fluid pressure limit. This peak force, orpressure limit, is made equal to the motor torque, pump pressure stalllimit. In producing the work stroke, the pump 10 has charged theaccumulator 32 to peak pressure P,. Under isothermal conditions, thework done in charging the accumulator 32 is =Pi 1 a/ 1) which statesthat the work available from the accumulator 32 is proportional to theproduct of the accumulator volume by the natural log of the compressedair volume ratio. At hydraulic pressures normally used, thus 500 3,000psi, energy to produce a starting torque sufficient for reliablereversal can easily be achieved.

Accordingly, when the stalled condition is reached, with the fullextension of work ram 40, the direction of the motor is reversed, andthe pump 10 now supplies fluid to the rod end 37 of the hydraulicactuator 35, as is shown by the direction of the arrows in FIG. 2. Thefluid discharge from the blind end 33 is now greater than the pump 10output into the rod end, so the excess must be diverted to the reservoir25. This is accomplished by the compensator shuttle valve 12, which nowsenses the hydraulic pressure on the rod end 37, closing poppet valve 16and the port associated therewith to maintain pressure, and openingpoppet valve 14 and its associated port to the reservoir 20.Accordingly, the pump 10 moves fluid from the blind end 33 to the rodend 37, with the excess being diverted through the open poppet valve 14to the reservoir 20. The compensator shuttle valve 12 thus functions tocontrol the flow of fluid from and to the reservoir 20 automaticallyregardless of fluid direction or direction of the work ram 40. Thediameter of the rod 38 or the piston 36 has no effect on the operationof the compensator valve 12, since the compensator shuttle valveposition is controlled by the pressure lines to the hydraulic actuator35.

For the continuous cyclic operation of the system shown in FIG. 1, thepiston 36 is allowed to touch bottom at the end of the return stroke,recharging the back side accumulator 32 and again reversing the motor70. This cycle is repeated as long as power is applied to the motor 70with no electrical or hydraulic switching. As has been previouslypointed out, the accumulators and their action depend on the flexibilityof the system, and additional accumulator action may be provided byproviding longer or larger diameter hoses or lines, or various otherbellows or spring/piston arrangements connected to the hydraulic lines.The system may be stopped by depressing the momentary stop switch 62 toremove power on the motor 70. A timer or other control means may beprovided and connected to the stop switch 62 to control the cyclicaloperation of the hydraulic system. As previously stated, once the systemhas been stopped, manual reversal may be achieved by pressing the manualreversal switch 76 along with start switch 60, which reverses theconnections to the starting winding 76 of the motor 70.

The work ram 40 may perform a plurality of functions. The hydraulicactuator 35 provides a means of amplifying or increasing the forceapplied to the work ram 40. The work ram may be used for cutting when adie is attached thereto, log splitting, pressure for extraction ofjuice, metal forming and cutting, or other pressing operations, such asgarbage compaction.

The hydraulic system described in FIGS. 1 and 2 may by utilized for avariety of applications, and the electrical control circuits for thesystem may vary in accordance with such applications. FIG. 3 provides anillustrative embodiment of another electric control circuit for a singlestroke return-and-stop operation. In this embodiment, a start switch 92is provided having contacts 93, 95, 97, 98 and 99 which, on activation,provide power to the starting winding 76 and the operating winding 74,but at the same time provide an automatic reversal of the startingwinding 76 when the start switch is released. The circuit in FIG. 3 alsoincludes a limit switch 90 which is shown in phantom on FIG. 2, merelyto show its positioning for actuation by the ram 40. The operation ofthe hydraulic system is the same as that shown in FIGS. 1 and 2. In theembodiment shown in FIG. 3, the motor 70 is started by momentarilydepressing the switch 92, which places starting current on the startingwinding 76 and power onto the operating winding 74 of the motor 70. Atthe instant the momentary starting switch 92 is released, the rotor 72of the motor 70 is up to speed, and the reversing connection on thestarting winding 76 is made, with the reverse connection having noeffect on direction of motor rotation or the power producing output.Again the motor size is selected which has the stall torque equivalentto the power required to produce maximum hydraulic pressure, or the ramforce desired. The motor 70 is already connected for reverse directionrotation, and a reverse torque is produced from a stalled or lockedposition. When the hydraulic ram 40 pressure reaches the stalled torquevalue, the motor rotor 72 is instantly at rest, producing startingtorque in the reverse direction. This stall condition occurs for afraction of a second, and almost immediately the motor 70 reverses andruns again until the ram 40 triggers the limit switch 90, whichinterrupts power to the motor 70, and the motor 70 shuts down. The startswitch 92 is a momentary on type because an operator is required only toenergize the system to initiate the forward stroke of the piston 36. Theoperator can release the switch 92 anytime after the limit switch 90 iscleared (approximately one second), and before the motor reaches thestall condition. Since the work stroke of the ram 40 is predominantlythe longer time period of the cycle, the deactivation of the limitswitch 90 is negligible. This operation minimizes operator error, and toactually damage the motor the operator must deliberately hold the switch92 while the motor is in a stalled condition. The limit switch is usedto automatically shut down the system after the cycle is completed. Inthis application, the back side accumulator 32 is not needed. The switch92, enabling the operator to start the motor in one direction andreverse the connections of the initial direction of the motor, makes iteasier to match the dynamics of the system to the load and makes iteasier to provide the automatic reversal feature with a variety ofdifferent types of motors and pumps.

The hydraulic control system of this invention offers a number ofadvantages relating to the reduction of parts, such as relief valves,directional valves, pressure switches, and the setting of centralpressures. Smaller size motors may be used, depending on theapplication, which will usually be one third of the size normallyrequired, which also provides a saving in power. A flywheel may also beused with the motor to provide additional inertia to operate larger workloads when required. With the reduced parts, maintenance problems areminimized due to component failure and breakdowns due to fluidcontamination. The smaller, compact package has greater application withreduced wire and plumbing lines, and the smaller system permits the useof a smaller reservoir. The smaller size is also more economical thanother equivalent type systems.

Since other modifications and changes, varied to fit particularoperating requirements and environments, will be apparent to thoseskilled in the art, the invention is not considered limited to theexamples chosen for purposes of disclosure, and covers all modificationsand changes which do not constitute departures from the true spirit andscope of this invention.

I claim:

1. A reversible motor-driven hydraulic control system comprising a. areversible pump,

b. a reservoir containing a source of fluid,

c. an actuator cylinder having a hydraulic piston movable in twodirections therein coupled to said reversible pump,

d. a compensator means coupled to said reservoir and between said pumpand said actuator cylinder for equalizing fluid displacement in saidactuator cylinder on the movement of said piston therein andreplenishment of fluid to the system,

. a reversible motor coupled to said reversible pump having a stalledtorque value substantially equivalent to the torque required to producea predetermined hydraulic pressure under load conditions on the pistonin said actuator cylinder, and

f. momentary switch means actuating said motor for rotation in onedirection until the hydraulic pressure reaches the stalled torque valuethereby producing a starting torque in the reversed direction andreversing the direction of rotation of said motor and the reversiblepump driven thereby.

2. The reversible motor-driven hydraulic control system set forth inclaim 1 wherein said compensator means comprises two opposing poppetvalves which are mechanically linked and three ports, one of which iscoupled to said reservoir and the other two associated with said opposedpoppet valves and coupled to opposite sides of said pump and said pistonin said actuator cylinder, said poppet valves being opened in accordancewith the hydraulic pressure in said system.

3. The reversible motor-driven hydraulic control system set forth inclaim 1 wherein said momentary switch means includes a latching relayand associated contacts across a source of power which applies startingcurrent to the start winding and power to an operating winding of saidmotor.

4. The reversible motor-driven hydraulic control system set forth inclaim 2 having a manual reversal switch means connected to the startwinding of said motor for reversing the connections to said startwinding whereby said motor may be reversed in direction of rotation byactuating said reversal switch means.

5. The reversible motor-driven hydraulic control system set forth inclaim 1 having a stop switch means in circuit with the contacts of saidlatching relay for releasing said latching relay and stopping saidmotor.

single stroke and return of said movable piston of said actuatorcylinder.

7. The reversible motor-driven hydraulic control system set forth inclaim 1 including accumulator means connected between said reversiblepump and actuator

1. A reversible motor-driven hydraulic control system comprising a. areversiBle pump, b. a reservoir containing a source of fluid, c. anactuator cylinder having a hydraulic piston movable in two directionstherein coupled to said reversible pump, d. a compensator means coupledto said reservoir and between said pump and said actuator cylinder forequalizing fluid displacement in said actuator cylinder on the movementof said piston therein and replenishment of fluid to the system, e. areversible motor coupled to said reversible pump having a stalled torquevalue substantially equivalent to the torque required to produce apredetermined hydraulic pressure under load conditions on the piston insaid actuator cylinder, and f. momentary switch means actuating saidmotor for rotation in one direction until the hydraulic pressure reachesthe stalled torque value thereby producing a starting torque in thereversed direction and reversing the direction of rotation of said motorand the reversible pump driven thereby.
 2. The reversible motor-drivenhydraulic control system set forth in claim 1 wherein said compensatormeans comprises two opposing poppet valves which are mechanically linkedand three ports, one of which is coupled to said reservoir and the othertwo associated with said opposed poppet valves and coupled to oppositesides of said pump and said piston in said actuator cylinder, saidpoppet valves being opened in accordance with the hydraulic pressure insaid system.
 3. The reversible motor-driven hydraulic control system setforth in claim 1 wherein said momentary switch means includes a latchingrelay and associated contacts across a source of power which appliesstarting current to the start winding and power to an operating windingof said motor.
 4. The reversible motor-driven hydraulic control systemset forth in claim 2 having a manual reversal switch means connected tothe start winding of said motor for reversing the connections to saidstart winding whereby said motor may be reversed in direction ofrotation by actuating said reversal switch means.
 5. The reversiblemotor-driven hydraulic control system set forth in claim 1 having a stopswitch means in circuit with the contacts of said latching relay forreleasing said latching relay and stopping said motor.
 6. The reversiblemotor-driven hydraulic control system set forth in claim 1 wherein saidmomentary switch means comprises a reversal switch for reversing theconnections to the start winding of said motor, limit switch meansconnected to said motor and actuated under control of said movablepiston of said actuator cylinder for removing power from said motorafter a single stroke and return of said movable piston of said actuatorcylinder.
 7. The reversible motor-driven hydraulic control system setforth in claim 1 including accumulator means connected between saidreversible pump and actuator cylinder.